Due to the demand for data communication and the increase in various communication services in wireless communication systems, there is a growing need to increase the transmission capacity of these wireless communication systems. To this end, technology for heterogeneous networks has been studied. The term ‘heterogeneous network’ may refer to a communication system in which cells having different phases, cell coverages and characteristics are operating in a mixed way.
A configuration of a conventional heterogeneous network will be described below with reference to FIG. 1.
FIG. 1 illustrates an example of a configuration of a conventional heterogeneous network. The heterogeneous network has a plurality of pico cells 102 to 106 additionally included in a cellular network 100 of a conventional macro cell. Although not illustrated, the cellular network 100 of the macro cell may include femto cells in addition to the pico cells.
This heterogeneous network may increase not only the overall transmission capacity of the system but also the transmission capacity in additional cells such as pico cells and femto cells, making it possible to provide additional services.
For the cells included in the heterogeneous network, different cell coverage sizes may be established depending on the purposes and environments of the cells, and/or because Base Stations (BSs) of the different cells may have different transmission (TX) powers. Inter-cell interference may occur between cells having different cell coverage sizes because their cell operating areas may overlap.
Inter-cell uplink (UL) interference in a conventional heterogeneous network will be described below with reference to FIG. 2.
FIG. 2 illustrates UL interference of a macro Mobile Station (MS) to a pico cell in a conventional heterogeneous network. It is assumed that in a heterogeneous network with one pico cell 240 included in a macro cell 200, a macro mobile station (MS) 220 in the macro cell 200 communicates with a macro base station (BS) 210 and a pico MS 250 in the pico cell 240 communicates with a pico BS 230.
The pico MS 250 may be influenced by significant interference from the macro MS 220, which is located relatively closer to the pico BS 230 than the macro BS 210, when the macro MS 220 transmits uplink (UL) signals. A common power control equation may be defined as,PTX=L+NI+SINRTarget   (1)
Equation (1) represents a common UL power control equation. In Equation (1), PTX represents UL transmit (TX) power, L represents a path loss, NI represents Noise and Interference (NI), and SINRtarget represents a target received Signal to Interference and Noise Ratio (SINR). As shown in Equation (1), conventionally, the UL TX power is determined by compensating for the path loss and the NI (or the amount of interference) in addition to the target received SINR.
The macro MS 220 located far from the macro BS 210 may have a large path loss that should be compensated for. Thus, the pico BS 230, which is located relatively closer to the macro MS 220, may undergo interference by UL signals that the macro MS 220 transmits with power higher than that of UL signals transmitted by the pico MS 250. Therefore, an effective method for reducing inter-cell interference due to TX power of UL signals in a heterogeneous network should be taken into consideration.